Warn when inout parameter is never written (#4777)

Addresses #4698 as one approach to diagnose the potential problem.

Emit warnings when a user marks a parameter as `inout` but never writes to it in the function. A new intrinsic function `unmodified(out T)` has been added to explicitly indicate that an `inout` variable will not be modified in the function.

This is only one way to address the specific validation error in #4698. In general it seems that DXC does some more extensive checks on actual struct fields (as opposed to observing arbitrary struct writes), so that will be the next step.

1 files changed, 1 insertions, 1 deletions

diff --git a/tests/autodiff/reverse-inout-param-custom-derivative.slang b/tests/autodiff/reverse-inout-param-custom-derivative.slang
index 8769a33c7..c4549e37b 100644
--- a/tests/autodiff/reverse-inout-param-custom-derivative.slang
+++ b/tests/autodiff/reverse-inout-param-custom-derivative.slang
@@ -5,7 +5,7 @@
 //TEST_INPUT:ubuffer(data=[0], stride=4):out,name=outputBuffer
 RWStructuredBuffer<float> outputBuffer;
 
-float rng(inout int state, float x)
+float rng(int state, float x)
 {
     return state + x;
 }